Online platforms are not common carriers, at least not according to Title II. Nor should they be. They shouldn't be forced to carry all content, and that's a good thing. 

Recent court cases in Florida and Texas have ruled this way, and the Supreme Court is due to write an opinion on the state-level rules that would have made it illegal to curate content on social media.

Removing the "right to censor" also means requiring blogs to host all comments and spam regardless of content.

The main issue on censorship and moderation stems from the jawboning at the hands of US agencies – directly or indirectly – which should absolutely be illegal.

Ultimately, nostr can win not because social media platforms will be "forced" to carry all content, but because online users will recognize that the censorious platforms suck and will choose to go elsewhere. I'd rather have that freedom to choose, and continue Section 230 as it applies to online platforms, than have the government make that determination. 

 Nobody is forced to host all content, they are just not a common carrier if they pick and choose (and thus are liable for the outcome of their editorial discretion). 

 Could that be applied to relay operators too though? 

 If you're selling relay hosting as a service, then yes
  
If your revenue stream is something else (or charitable), then no 

 Even common carriers do some censorship, for example they filter spam. So where is the line the drawn? 

 I don't see how you can draw the line at anything other than "does not filter" vs "does filter" if you're trying to be consistent (which the law purportedly is) 

 Actually I am not sure if common carriers filter spam. Anyeays, social media or any other type of platform cannot possibly be called a common carrier, as there is a pretty clear distinction between displaying content versus providing the pipes over which content travels.